Part of the fun for me when building an amp is hunting down cool parts. I try to find as many vintage parts as I can, but then I combine these with some modern items for dependability and functionality. I have scored some holy grail parts already but I still need to fill in some gaps. There is a certain mystique associated with vintage parts. Amp builders call it “mojo.” While the older parts often pale in comparison spec-wise and noise-wise to modern parts, builders use them to come as close as they can to the original tone and dare I say soul of the original Plexi and JTM45 amplifiers. The parts are expensive but my idea is to build this amp once and it will be the last amp I ever own. Here are some of the parts I have acquired:
1970s Mullard “Mustard” Capacitors – These are a must when seeking the tone, feel and look of a vintage Marshall amp. I found these N.O.S. (New Old Stock) on eBay from a seller in Greece. I still need to find a .68uF 160 volt which is pretty tough to do. They look like mustard from a squeeze bottle, hence the name.
Radiospares 560pF Capacitors – I had one of these already that I bought a long time ago, but I need 2 for the build. One is for the bright channel mix capacitor and the other for treble tone stack. I found one from a seller in France on the Metroamp Forum. paid a bunch. Ouch.
Carling Switches with Plexi-style Chrome Toggle Rings – These were both readily available on the Valvestorm.com site, a very cool place to find Marshall parts.
Piher Resistors – These are the same brand of resistors used in Marshall JMP and JCM800 amps of the late 70’s and early 80’s. I sourced them from guys in France and Spain. The 1/2 watt ones I found are from the 60s and 70s while the 2 watters are 90s vintage. I am still missing 2K7 and 4K7 values in 1/2 watt. The hunt continues…
Lemco Dogbone 47pF – This will be the phase inverter capacitor. Valvestorm.com
BC 10uF 160 volt – I found some 400 volt versions on eBay.uk that I was going to use but then I stumbled on the proper 160 volt versions at Valvestorm. These will be in the bias capacitor positions.
Belling Lee Fuse Holders – Very cool N.O.S. fuse holders I found on eBay from a guy in Pulborough, England.
ARS Dual Can Capacitors – These beauties will serve as the filter capacitors. When filter caps sit for a while they need to be reformed. These are sold reformed from Valvestorm.com.
1K 7watt Welwyn W22 Wirewound Resistors – These will live in the screen resistor position on each power tube socket. Very cool classic resistors from Valvestorm.
Metroamp 50 Watt Plexi chassis – This build is being done on a standard 50 watt Plexi chassis. The original JCM800 amplifiers had a much longer chassis. I want to keep the build compact so I am going with a the smaller chassis. On my previous JCM800 amps I used this same sized chassis as well. Once again – Valvestorm.com.